The present invention relates to an ultrasonic transducer having a pot-like casing.
European Patent Application No. 0 075 302 describes an ultrasonic transducer having a pot-shaped casing. On the inside, a piezoceramic vibrating element is mounted on the bottom of the pot. To dampen harmonics and shape the propagation and reception beams of this arrangement, arc-shaped damping elements are mounted on two opposing sides on the inside of the pot-shaped transducer casing. For mounting, the ultrasonic transducer is inserted into a casing made of soft plastic or soft rubber. One disadvantage of this design is that not only the diaphragm but also the casing wall. are excited to vibration due to the uniform wall thickness of the pot-shaped casing, which thus has a negative effect on both the transmission and reception beams or may even suppress them due to superimposed harmonics.
The ultrasonic transducer according to the present invention has the advantage that a greater rigidity of the casing is achieved due to the stabilizing ring on the wall of the pot-like casing, so the remaining part of the bottom area of the casing functions as a vibrating diaphragm, preferably vibrating at the fundamental wave. It is advantageous that the post-pulse oscillation time of the vibrating diaphragm is shortened because of the greater mass of the wall, advantageously yielding better propagation and reception beams on the whole as well as better vibration characteristics. In particular, a distance measurement, e.g., in a parking aid for a motor vehicle, can still be performed even at very small distances from an obstacle due to the shortened post-pulse oscillation time.
It is also advantageous that due to the remote arrangement of the stabilizing ring from the wall of the vibrating diaphragm, the sensor head can be reduced to minimal installation dimensions, so that after installation in a bumper, for example, an optimum appearance is achieved without any disturbing effect.
The stabilizing ring is formed at the time of manufacture of the casing, so the manufacturing costs are relatively low.
To shape the propagation beam in an advantageous manner, a sound directing device is arranged on the outside of the wall in the area of the vibrating diaphragm. Depending on the intended purpose, the sound directing device may be designed in such a way as to obtain the broadest propagation beam in the horizontal direction and the narrowest possible propagation beam in the vertical direction. The sound directing device is designed as a ring and includes the vibrating diaphragm. In addition, with an appropriate design of the sound directing device, it is also advantageous for the range of the ultrasonic transducer to be selectable.
To give an unobtrusive appearance, the sound directing device is preferably designed to be flush with the plane of the vibrating diaphragm. In an alternative embodiment, the sound directing can also be designed in a conical shape to have an even greater influence on the propagation and reception beams of the ultrasonic waves. To create better installation conditions, the cross section of the sound directing device is either rectangular or conical in shape.